Autoimmune diseases include disorders involving dysfunction of the immune system, which mediates tissue damage. Any organ may be affected by such processes through precipitation of immune complexes, cellular immunity, or inappropriate generation or action of immuno-hormones such as cytokines. Epidemiologically, autoimmune diseases are significant because of the numbers of patients that they affect and the serious morbidity and mortality that they cause. Common chronic systemic diseases in this group include diabetes mellitus, thyroid disease, rheumatoid arthritis, systemic lupus erythmatosus (SLE), primary antiphospholipid syndrome (APS), and a variety of diseases that affect the central nervous system. Neurological autoimmune diseases include disorders specific to the nervous system such as myasthenia gravis, Lambert Eaton myasthenic syndrome, Guillain-Barre syndrome, polymyositis, and multiple sclerosis. In addition, there are neurological complications of the systemic autoimmune diseases. Factors predisposing to autoimmune diseases include genetic predisposition and environmental agents such as certain infections and pharmaceutical products. Such factors result in pathological activation of the immune response in susceptible individuals, which is generally controlled by T lymphocytes (T cells). The activation of T cells and B subtypes, involves a complex interaction of cell surface receptors resulting in equally complex signal transduction pathways which eventually affect gene regulation. Full activation of lymphocytes requires parallel stimulation of several signal transduction pathways. See Ohtsuka et al., Biochim. Biophys. Acta. 1310:223-232 (1996).
Although there is growing understanding about the function of T cells in the immune response, this knowledge has not explained the basis of most autoimmune diseases. There are still questions to be resolved such as how tolerance to self in normal individuals is maintained; how tolerance is broken in autoimmunity; and which autoantigens trigger the immune system to produce specific diseases. A recent review by V. Taneja and C. S. David (J. Clin. Invest. 101:921-926 (1998)) provides an overview of important issues in this field and emphasizes how the generation of transgenic mice expressing functional HLA molecules is important for understanding the function of certain molecules in the induction of autoimmune disease, as well as circumvention of the xenogenic barrier. Regardless of the mechanisms involved in induction of autoimmune disease or the rejection of grafts, the common pathway for these events includes activation of a relatively small number of T lymphocytes.
Several immunosuppressive and immunomodulating treatments have been tested and subsequently applied in the treatment of autoimmune diseases. Gana-Weisz, M., HaMai, R., Marciano, D., Egozi, Y., Ben-Baruch, G., and Kloog, Y. The Ras antagonist S-farnesylthiosalicylic acid induces inhibition of MAPK activation. Biochem. Biophys. Res. Commun. 1997; 239: 900-904; Marciano, D., Aharonson*, Varsano, T., Haklai, R., and KO, Y. Novel inhibitors of the prenylated protein methyltransferase reveal distinctive structural requirements. Bioerg. Med. Chem. Lett. 1997; 7, 1709-1714; Paterson P. Y. (1978) The demyelinating diseases: clinical and experimental studies in animals and man. In: Immunological Diseases, 3rd Edition, (ed. by M. Smater, N. Alexander, B. Rose, W. B. Sherman, D. W. Talmage and J. H. Vaughn) p. 1400. Little, Brown and Company, Boston.
The main drawback of immunosuppressive modalities is that the induction of generalized suppression of all T-cells and immune functions is associated with long-term and cumulative side effects. In addition, it is now believed that broad suppression of immune cells may also cancel or neutralize the potential beneficial effects of down-regulatory cells such as suppressors and suppresor inducers or cytokines such as IL-10, on the autoimmune lymphocytes. Karussis, et al., supra; Gana-Weisz, et al., supra, Lieder, O., T. Reshef, E. Berauud, A. Ben-Nun, and I. R. Cohen. 1988, Anti-idiotypic network induced by T cell vaccination against experimental autoimmune encephalomyelitis, Science 239:181; Varela, F. J., and A. Coutinho, 1991, Second generation immune networks, Immunol. Today 12:159; Cohen, I. R., and D. B. Young. 1991, Autoimmunity, microbial immunity and the immunological homunculus, Immunol. Today 12:105; Lehmann, D., D. Karussis, R. Mizrachi-Koll, A. S. Linde, and O. Abramsky, 1997, Inhibition of the progression of multiple sclerosis by linomide is associated with upregulation of CD4+/CD45RA+ cells and downregulation of CD4+/CD45RO+ cells, Clin Immunol Immunopathol 85:202.
Therefore, current approaches for the treatment of autoimmune diseases advocate the use of immunomodulators or specific immunosuppressing medications. The goal of such research is specific suppression of only the lymphocytes with the autoimmune potential. The search for such specific suppressors is a formidable challenge, particularly considering the complex networks of signal transduction pathways associated with lymphocyte growth and differentiation, where many such pathways are common to all lymphoid lineages and to other cells.
In addition to autoimmune disease, there are several other diseases in which proliferation of normal cells other than T-cells constitutes part of the pathology.